ObjectiveTo develop and validate a nomogram for predicting overall survival among patients with breast apocrine carcinoma (BAC). MethodsThe patients diagnosed with BAC from 2010 to 2016 were selected from the Surveillance, Epidemiology, and End Results (SEER) database and then randomly divided into a training set and a validation set by a 7∶3 ratio. Additionally, external validation of the nomogram was conducted on BAC patients admitted to the Dongfeng Hospital Affiliated to Hubei Medical College from January 1, 2010 to December 31, 2018. The risk factors affecting the overall survival of BAC patients were determined by univariate and multivariate Cox regression analyses, which were used to develop the nomogram prediction model. The discriminative abilities of the nomogram for the 3- and 5-year overall survival rates were evaluated by the C-index and area under receiver operating characteristic curve (AUC), and the fit of actual data and nomogram-predicted data for calibrators should be evaluated. ResultsA total of 649 BAC patients who met the included criterion for this study were enrolled from the SEER database (including 454 in the training set and 195 in the internal validation set), and 21 BAC patients from the Dongfeng Hospital (external validation set) were included. The multivariate Cox regression analysis showed that the age, T stage, M stage, S stage, surgical method, and chemotherapy were the risk factors affecting the overall survival of BAC patients. The C-index values of the nomogram prediction model based on these risk factors was 0.76, 0.77, and 0.88 in the training set, internal validation set, and external validation set, respectively. The calibration curves of the actual 3- and 5-year overall survival rates and nomogram-predicted 3- and 5- year overall survival rates were close to the ideal curve. The AUCs (95%CI) of the nomogram prediction model for evaluating the 3-year and 5-year overall survival rates of BAC patients were 0.84 (0.78, 0.89) and 0.76 (0.71, 0.83) in the training set, 0.81 (0.73, 0.91) and 0.84 (0.77, 0.91) in the internal validation set, and 0.80 (0.70, 0.91) and 0.84 (0.76, 0.91) in the external validation set, respectively. ConclusionNomogram based on the SEER database to predict the overall survival of BAC patients has a good predictive effect for BAC patients.